A number of studies centering around the identification and composition of schistosome antigens as well as the response of the host to parasite antigens are in progress. A series of experiments were performed in order to study the control of release of schistosome excretory-secretory (E-S) substances in vitro following incorporation of labelled N-acetyl-glucosamine. The processes involved are complex and multiple, inhibited by Na flouride, colchcine, carbachol, and secretions from other schistosomes. Damage to the schistosome secretory processes are most likely dependent on energy metabolism, microtubular function and worm movement. Identification of large and small molecular weight E-S products of adult S. mansoni and B. malayi microfilaria continue. IgG ELISA antibody to a glycoprotein fraction of adult worms in infected patients was found to correlate with intensity of infection. Clinical studies involving G. lamblia trophozoites obtained from duodenal aspirates of patients as well as the specific antibody responses of the host to the parasite have been initiated.